logging: Add uart backend dependency to shell uart backend

If shell UART backend was enabled and logger uart backend was
not explicitly disabled then both were used resulting in logs
being printed twice on terminal.

Patch modifies default state of log uart backend to depend on
state of shell uart backend.

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>
3 files changed